How to loop material node animation?
To see the keyframes in the Graph editor select the object that has the keyframes.

To make a loop:

Press N to access the modifiers tab int he Graph editor. Then create a cycle.

That will create a loop for the keyframes automatically.



If you want to interrupt the cycle or make it start at a particular frame, play with the values for the Before and Ater.

A different way to do the same is using the Channel Extrapolation mode and set it to cycle.